"""platform/images — pure image processing (SD-0002 §6.2).

Model-free, deterministic, no I/O of its own: decode bytes, enforce the
resolution bar (INV-18 / Q-3), and emit downscale-only WebP renditions. The
caller (the image-fetch phase) owns fetching, storage, and status.
"""
from __future__ import annotations

import io
from dataclasses import dataclass

from PIL import Image, UnidentifiedImageError

# Q-3 (SD-0002 §13): the minimum shorter-side dimension; below it an image is
# rejected_low_res. Rejects icons/thumbnails, accepts normal product photos.
MIN_IMAGE_SHORT_SIDE = 500

# Rendition longest-side caps (px); downscale-only — a smaller source is kept
# at its own size, never upscaled. Encoded WebP.
RENDITIONS = {"thumb": 160, "card": 480, "detail": 1600}

# Source formats we accept (Pillow format names).
_ACCEPTED = {"JPEG", "PNG", "WEBP"}

_WEBP_QUALITY = 82


@dataclass(frozen=True)
class Processed:
    source_format: str
    width: int
    height: int
    renditions: dict[str, bytes]  # name -> WebP bytes


@dataclass(frozen=True)
class Rejected:
    reason: str  # "rejected_low_res" | "rejected_not_image"


def process(data: bytes) -> Processed | Rejected:
    """Decode + bar-check + renditions, or a typed rejection. Never raises on
    bad input — undecodable/unsupported bytes are Rejected('rejected_not_image')."""
    try:
        with Image.open(io.BytesIO(data)) as im:
            im.load()
            source_format = im.format or ""
            if source_format not in _ACCEPTED:
                return Rejected(reason="rejected_not_image")
            rgb = im.convert("RGB")
            width, height = rgb.size
            if min(width, height) < MIN_IMAGE_SHORT_SIDE:
                return Rejected(reason="rejected_low_res")
            renditions = {
                name: _rendition(rgb, cap) for name, cap in RENDITIONS.items()
            }
            return Processed(
                source_format=source_format,
                width=width,
                height=height,
                renditions=renditions,
            )
    except (UnidentifiedImageError, OSError, ValueError, Image.DecompressionBombError):
        return Rejected(reason="rejected_not_image")


def _rendition(rgb: Image.Image, cap: int) -> bytes:
    longest = max(rgb.size)
    if longest > cap:
        scale = cap / longest
        size = (max(1, round(rgb.width * scale)), max(1, round(rgb.height * scale)))
        resized = rgb.resize(size, Image.LANCZOS)
    else:
        resized = rgb
    buf = io.BytesIO()
    resized.save(buf, format="WEBP", quality=_WEBP_QUALITY, method=6)
    return buf.getvalue()